function s1_generate_a_series_of_files(){
   for i in {1..100};
   do echo $i>/tmp/new_file$i;
   done
}
function s2_list_4_files_in_long_format_about_account_and_group(){
   ls -l /etc/{passwd,shadow,group,gshadow} |sort -d
}
function s3_find_items_related_to_given_username(){
   grep -h "$1" /etc/{passwd,shadow} |sort -d
}
function s4_find_items_related_to_given_group_name(){
   grep -h "$1" /etc/{group,gshadow} |sort -d
}
function s5_create_groups_for_given_group_names(){
   groupadd rnd && groupadd itoperation
}
function s6_create_users_and_set_their_group_as_required(){
   useradd -G rnd adam && useradd -G rnd bob && useradd -G itoperation calvin && useradd -G itoperation david && useradd -G rnd edward
}
function s7_change_users_shell(){
   usermod -s /usr/bin/sh adam && usermod -s /usr/bin/sh edward
}
function s8_set_password_change_policy(){
   passwd -n 10 -x 60 -w 10 adam
   passwd -n 10 -x 60 -w 10 bob
   passwd -n 10 -x 60 -w 10 david
   passwd -n 10 -x 60 -w 10 calvin
   passwd -n 10 -x 60 -w 10 edward
}
function s9_set_password_for_five_users(){
   local usernames=(adam bob calvin david edward)
   local -n passwords=("$@")
   for i in "${!usernames[@]}"; do
       echo "${usernames[i]}:${passwords[i]}" | chpasswd
   done
}
function s10_lock_bobs_password(){
   usermod -L bob
}
function s11_include_adam_into_wheel_group(){
   usermod -a -G wheel adam
}
function s12_change_files_permission(){
   for i in {1..33};
   do
      file="/tmp/new_file$((3*i))"
      if [ -f "$file" ]; then
          chmod -R 640 "file"
      fi
   done
}
